“Active tip clearance control” refers to a gas turbine engine system wherein the radial gap between the turbine blades and surrounding static shroud is varied during the engine cycle in order to optimize tip clearance. Active tip clearance control (ATCC) typically uses compressor or bypass air to selectively cool the turbine shrouds to affect tip clearance. The compressor outlet air (sometimes referred to as “P3” air) usually has a relatively high temperature and a large volume of compressor air is thus required to achieve an effective cooling of the turbine shroud, which is therefore relatively thermodynamically “expensive” for the engine. The use of bypass air for ATCC may be preferred because of its relatively lower temperature, however, bypass air is at a much lower pressure than P3 air, making it more sensitive to pressure losses within the ATCC system. These and other problems indicate the need to provide improved ATCC systems.